New centralized version, runs on ops. Monitors all paths for the experiment

and issues tevc commands to delay nodes. This version will look in the user
environment for plab nodes if they are not actually allocated to the
experiment. This enables use of the no_plab option in the NS file so plab
nodes are not actually allocated to the experiment.
Can still get the per-node version with -r.
The centralized version uses bgmon (managerclient) to crank up the frequency
at which measurements are made.